fix: send Last.fm now-playing notification when track starts

Add POST /api/player/lastfm/now-playing call on every track start via
onTrackStarted callback in PlayerManager, matching other clients.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

furumi_macos/CatalogService.swift

@@ -190,6 +190,12 @@ struct CatalogService {
         _ = try await post(path: "api/player/devices/command", body: body)
     }
 
+    func lastfmNowPlaying(trackId: Int64) async throws {
+        struct Body: Encodable { let trackId: Int64 }
+        let body = try Self.deviceEncoder.encode(Body(trackId: trackId))
+        _ = try await post(path: "api/player/lastfm/now-playing", body: body)
+    }
+
     func recordHistory(trackId: Int64, startedAt: Int64?, durationListened: Int32, completed: Bool) async throws {
         struct Body: Encodable {
             let trackId: Int64

furumi_macos/ContentView.swift

@@ -106,6 +106,9 @@ struct ContentView: View {
         Task { await authManager.loadLikedIds() }
         deviceManager.start(service: service, player: player)
         let am = authManager
+        player.onTrackStarted = { trackId in
+            try? await am.catalogService?.lastfmNowPlaying(trackId: trackId)
+        }
         player.onTrackFinished = { trackId, startedAt, durationListened, completed in
             guard let svc = am.catalogService else { return }
             try? await svc.recordHistory(trackId: trackId, startedAt: startedAt, durationListened: durationListened, completed: completed)

furumi_macos/PlayerManager.swift

@@ -37,6 +37,7 @@ final class PlayerManager {
     var canGoPrevious: Bool { currentIndex > 0 }
     var formattedCurrentTime: String { formatTime(currentTime) }
 
+    var onTrackStarted: ((Int64) async -> Void)?
     var onTrackFinished: ((Int64, Int64?, Int32, Bool) async -> Void)?
 
     private var player: AVPlayer?
@@ -102,6 +103,8 @@ final class PlayerManager {
 
         addObserver()
         updateNowPlayingInfo(track: track)
+        let cb = onTrackStarted
+        Task { await cb?(track.id) }
     }
 
     // MARK: - Public playback